1. Field of the Invention
The present invention relates in general to starch-based corrugating adhesive compositions, and more particularly, to starch-based corrugating adhesive compositions which, among other things, utilize an undried carrier starch as a component thereof.
2. Background Art
Adhesives for use in association with corrugating applications have been known in the art for years, and are the subject of numerous patents, including: U.S. Pat. No. 4,978,411 entitled xe2x80x9cPROCESS OF USING STARCH BASED CORRUGATING ADHESIVES;xe2x80x9d U.S. Pat. No. 4,912,209 entitled xe2x80x9cSTARCH BASED CORRUGATING ADHESIVES;xe2x80x9d U.S. Pat. No. 4,787,937 entitled xe2x80x9cHIGH SOLIDS CORRUGATING ADHESIVE;xe2x80x9d U.S. Pat. No. 4,769,096 entitled xe2x80x9cPROCESS OF BONDING FLUTED FILTER MEDIA TO END CAPS;xe2x80x9d U.S. Pat. No. 4,568,714 entitled xe2x80x9cCORRUGATING ADHESIVE COMPOSITION FOR ADHERING NORMALLY ADHERENT SURFACES;xe2x80x9d U.S. Pat. No. 4,424,291 entitled xe2x80x9cCORRUGATING ADHESIVE COMPOSITION AND PAPERBOARD PRODUCT PRODUCED THEREWITH;xe2x80x9d U.S. Pat. No. 4,400,480 entitled xe2x80x9cPROCESS FOR PREPARING CORRUGATED PAPERBOARD;xe2x80x9d U.S. Pat. No. 4,366,275 entitled xe2x80x9cWATER-RESISTANT ALKALINE CORRUGATING ADHESIVE COMPOSITION;xe2x80x9d U.S. Pat. No. 4,359,341 entitled xe2x80x9cSTARCH BASED ADHESIVES AND METHOD THEREFORE;xe2x80x9d and U.S. Pat. No. 4,018,959 entitled xe2x80x9cCORRUGATING ADHESIVE COMPOSITION CONTAINING THERMOPLASTIC POLYMER, THERMOSETTING RESIN, AND STARCHxe2x80x9d all of which are hereby incorporated herein by reference in their entirety.
U.S. Pat. Nos. 4,978,411, and 4,912,209 disclose starch-based alkaline corrugating adhesives and processes for using the same, which purportedly have improved green bond strength due to the use of undried starch as the raw (non-carrier) starch component in the adhesive. Such adhesives can purportedly be used in corrugation processes at much higher corrugator running speeds than conventionally employed adhesives.
U.S. Pat. No. 4,787,937 discloses an alkaline-curing, starch-based corrugating adhesive employing ungelatinized tapioca starch and a carrier comprising high amylose starch, wherein the total solids of the adhesive is from 30 to 45% solids by weight. The disclosed adhesives purportedly provide improved tack and corrugator running speeds.
U.S. Pat. No. 4,769,096 discloses a fluted filter media to end cap bonding process. The process comprises coating at least one end cap and/or at least one fluted edge of the filter media with a bonding composition, contacting the end cap with the edge of the fluted filter media, and curing the bonding composition coating to form a strong, continuous filter media to end cap bond. The bonding composition comprises, an adhesive latex, a thermoplastic resin, and an amount of ungelatinized granular starch effective to complex a major portion of the latex water during curing of the bonding composition.
U.S. Pat. No. 4,568,714 discloses an aqueous starch-based corrugating adhesive containing casein xe2x80x94a carboxylated styrene-butadiene copolymer latex. Preferably glyoxal is used to adhere liner and medium substrates having normally adherent surfaces.
U.S. Pat. No. 4,424,291 discloses a corrugating adhesive composition which purportedly exhibits superior tack performance by replacing, on a solids basis, from 5 to 100%, by weight, of the gelatinized starch carrier of a typical known starch-corrugating adhesive with a polymer containing at least 10%, by weight, of carboxyl groups derived from a polymerizable ethylenically unsaturated mono- or polycarboxylic acid or a mixture of these polymers.
U.S. Pat. Nos. 4,400,480 and 4,366,275 disclose a crosslinking additive for imparting water resistance to starch-based corrugating adhesive compositions which is prepared by: (a) reacting acetone and formaldehyde under aqueous alkaline conditions at 20 degrees to 80 degrees Centigrade in a molar ratio of 1 mole acetone to about 2 to 5.5 moles formaldehyde; (b) adding to the reaction mixture at least an effective amount of dihydroxyethylene urea to scavenge the free formaldehyde in the mixture; and (3) reacting until the amount of unreacted formaldehyde remaining is reduced to about 0.1-2%. The crosslinking additive thus obtained, which is low in free formaldehyde, may be added directly to a starch-based corrugating adhesive or may be first mixed with dimethylol dihydroxyethylene urea.
U.S. Pat. No. 4,359,341 discloses a process for preparing a carrier type starch which is characterized by the steps of mixing two starch portions having different gelatinization temperatures with water to form a slurry and causing gelatinization of the starch portion having the lower gelatinization temperature to thereby form a stable gelatinized carrier for the raw starch portion having the higher gelatinization temperature. The ratio of the starch portion having the lower gelatinization temperature to the starch portion having the higher gelatinization temperature is preferably of the order of from 1:10 to 1:4 and the ratio by weight of the starch portions to water is of the order of from 1:2 to 1:4, preferably about 1:3. A carrier type starch based adhesive comprising a mixture of a gelatinized carrier starch portion and a raw starch portion having a higher gelatinization temperature dispersed in the carrier portion is also disclosed.
U.S. Pat. No. 4,018,959 discloses improved adhesive compositions which are useful in the manufacturing of corrugated boards comprising a mixture of: (a) a crosslinkable water dispersible polymer, (b) an ungelatinized starch, (c) a urea-formaldehyde resin, (d) an acidic metal salt, and (e) water.
While the above-identified references do appear to provide operable adhesives for corrugating applications, their compositions do not efficiently utilize components which cost effectively facilitate adhesive uniformity, adhesive consistency, personnel reduction in adhesive production, and/or safety. For example, using dried starch as a carrier starch can materially increase overall adhesive costs because the energy necessary to run dryers is substantial, which in a low margin industry becomes significant.
It is therefore an object of the present invention to provide a starch-based corrugating adhesive composition having an undried carrier starch as a component thereof, which, among other things, remedies the aforementioned detriments and/or complications associated with the use of the above-identified corrugating adhesives.
The present invention is directed to a starch-based corrugating adhesive composition comprising: (a) at least one solvent, such as water; (b) a carrier starch dispersed within the at least one solvent, wherein the carrier starch is undried; (c) a raw starch dispersed within the at least one solvent; and (d) wherein the starch-based corrugating adhesive composition comprises a pH of greater than approximately 7.
In a preferred embodiment of the present invention, the at least one solvent is present in a concentration ranging from approximately 60 percent to approximately 85 percent by weight of the total adhesive composition.
In another preferred embodiment of the present invention, the carrier starch may be viscosity modified (by e.g. cooking, peptizing, acid hydrolysis, oxidation, etc.), at least partially cooked, peptized, and combinations thereof.
In yet another preferred embodiment of the present invention, the carrier starch is selected from the group consisting of undried corn starch, undried tapioca starch, undried rice starch, undried potato starch, undried wheat starch, undried sago starch, and mixtures thereof. In this embodiment, the carrier starch may comprise undried starch milk and/or the carrier starch may be exposed to ambient temperature and pressure, and therefore xe2x80x9cair dried.xe2x80x9d
Preferably, the carrier starch is selected from the group consisting essentially of native corn starch, hybrid amylose corn starch, hybrid amylopectin corn starch, and mixtures thereof.
In another aspect of the present invention, the carrier starch is present in a concentration ranging from approximately 2.5 percent to approximately 18 percent by weight of the total starch composition, and more preferably from approximately 3 percent to approximately 7.5 percent by weight of the total starch composition.
In accordance with the present invention, the raw starch may be dried or undried, and, similarly to the carrier starch, selected from the group consisting of undried corn starch, undried tapioca starch, undried wheat starch, undried potato starch, undried wheat starch, undried sago starch, and mixtures thereof.
In a preferred embodiment of the present invention, the raw starch is present in a concentration ranging from approximately 15 percent to approximately 95 percent by weight of the total starch composition, and more preferably from approximately 70 percent to approximately 85 percent by weight of the total starch composition.
The present invention also discloses incorporating a basic additive into the adhesive composition, such as LiOH, NaOH, KOH, RbOH, CsOH, FrOH, Be(OH)2, Mg(OH)2, Ca(OH)2, Sr(OH)2, Ba(OH)2, Ra(OH)2, and mixtures thereof. In this embodiment, the basic additive is preferably present in a concentration ranging from approximately 0.1 percent to approximately 2 percent by weight of the total adhesive composition.
The present invention further discloses incorporating borax and/or boric acid into the adhesive composition. In this embodiment, the borax and/or boric acid is present in a concentration ranging from approximately 0.1 percent to approximately 2 percent by weight of the total adhesive composition.
In a preferred embodiment of the present invention, the ratio of raw starch to carrier starch ranges from approximately 3/1 to approximately 25/1 by weight of the total adhesive composition and/or the total solid content of the adhesive composition ranges from approximately 15 percent to approximately 40 percent by weight based on the total weight of the mixture.
The present invention is also directed to a starch-based corrugating adhesive composition comprising: (a) at least one solvent; (b) a carrier starch dispersed within the at least one solvent, wherein the carrier starch is undried; (c) a raw starch dispersed within the at least one solvent, wherein the carrier starch is undried; and (d) wherein the starch-based corrugating adhesive composition comprises a pH of greater than approximately 7.
The present invention is further directed to a starch-based corrugating adhesive composition comprising: (a) at least one solvent, wherein the at least one solvent comprises water, and further wherein the at least one solvent is present in a concentration ranging from approximately 60 percent to approximately 85 percent by weight of the total adhesive composition; (b) a carrier starch dispersed within the at least one solvent, wherein the carrier starch is undried, and further wherein the carrier starch is at least partially cooked, peptized, and combinations thereof, and further wherein the carrier starch is present in a concentration ranging from approximately 2.5 percent to approximately 18 percent by weight of the total starch composition; (c) a raw starch dispersed within the at least one solvent, wherein the raw starch is present in a concentration ranging from approximately 15 percent to approximately 95 percent by weight of the total starch composition; and (d) wherein the starch-based corrugating adhesive composition comprises a pH of greater than approximately 7.